Experts are skeptical of the threat posed by a reported design flaw in Microsoft Active Directory, which is used by many enterprises to control employee access to the corporate network.

Israeli security firm Aorato reported Monday that it created a proof-of-concept attack in which it was able to change a person's network password, thereby making it possible to access other sensitive systems.

Aorato claims the problem stems from Active Directory's backward compatibility with an authentication protocol called NTLM that was the default in versions of Windows older than Windows XP SP3.

Newer versions of Windows use a more secure protocol called Kerberos, which Microsoft has been encouraging customers to upgrade to for years.

NTLM is vulnerable to a so-called "pass-the-hash" attack in which an attacker steals the login credentials for a computer and then uses the hash for those credentials in changing a user's password. The new password can then be used to access other services, such as remote desktop protocol (RDP) or the Outlook web application.

Microsoft says Aorato has not shown anything new.

"This is a well-known industry limitation in the Kerberos Network Authentication Service standard," the company said in a statement sent to CSOonline Tuesday. "Information on how to manage this limitation when using Windows can be found on the Microsoft TechNet site."

Security experts agreed that the problem is not a major risk for businesses.

"It does not seem to be as serious as pictured since the conditions where an actual attack can happen are very complex," Ehsan Foroughi, director of research at Security Compass, said.